Comparison of modern analysis approaches based on the postulated GDH blockage event at Ignalina NPP

The paper presents an analysis of the postulated blocking of coolant flow rate in Group Distribution Header event at the Ignalina NPP. Two types of analysis-best estimate and partially-conservative -are performed. The best-estimate approach is based on the best-estimate codes with realistic boundary and initial conditions plus uncertainty analysis, while partially-conservative approach is based on the best estimate codes with conservative boundary and initial conditions plus conservative assumptions. A comparison of both calculations showed that the peak fuel cladding temperatures for best-estimate calculation, taking into account the uncertainty analysis, is slightly lower in comparison with partially-conservative calculation. The partially-conservative approach requires considerably less computational time. However, when with this methodology obtained results do not meet acceptance criteria (as it was in this particular case), a complete analysis employing the best-estimate approach is necessary. (author)